The TDX guest platform takes one bit from the physical address to
indicate if the page is shared (accessible by VMM). This bit is not part
of the physical_mask and is not preserved during mprotect(). As a
result, the 'shared' bit is lost during mprotect() on shared mappings.
_COMMON_PAGE_CHG_MASK specifies which PTE bits need to be preserved
during modification. AMD includes 'sme_me_mask' in the define to
preserve the 'encrypt' bit.
To cover both Intel and AMD cases, include 'cc_mask' in
_COMMON_PAGE_CHG_MASK instead of 'sme_me_mask'.
Signed-off-by: Kirill A. Shutemov <[email protected]>
Fixes: 41394e33f3a0 ("x86/tdx: Extend the confidential computing API to support TDX guests")
Cc: Tom Lendacky <[email protected]>
Cc: Chris Oo <[email protected]>
Cc: Dexuan Cui <[email protected]>
---
arch/x86/include/asm/pgtable_types.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
index 3f648ffdfbe5..7dd2fdfacff3 100644
--- a/arch/x86/include/asm/pgtable_types.h
+++ b/arch/x86/include/asm/pgtable_types.h
@@ -148,7 +148,7 @@
#define _COMMON_PAGE_CHG_MASK (PTE_PFN_MASK | _PAGE_PCD | _PAGE_PWT | \
_PAGE_SPECIAL | _PAGE_ACCESSED | \
_PAGE_DIRTY_BITS | _PAGE_SOFT_DIRTY | \
- _PAGE_DEVMAP | _PAGE_ENC | _PAGE_UFFD_WP)
+ _PAGE_DEVMAP | _PAGE_CC | _PAGE_UFFD_WP)
#define _PAGE_CHG_MASK (_COMMON_PAGE_CHG_MASK | _PAGE_PAT)
#define _HPAGE_CHG_MASK (_COMMON_PAGE_CHG_MASK | _PAGE_PSE | _PAGE_PAT_LARGE)
@@ -173,6 +173,7 @@ enum page_cache_mode {
};
#endif
+#define _PAGE_CC (_AT(pteval_t, cc_mask))
#define _PAGE_ENC (_AT(pteval_t, sme_me_mask))
#define _PAGE_CACHE_MASK (_PAGE_PWT | _PAGE_PCD | _PAGE_PAT)
--
2.43.0
On Fri, 2024-04-12 at 22:12 +0300, Kirill A. Shutemov wrote:
> The TDX guest platform takes one bit from the physical address to
> indicate if the page is shared (accessible by VMM). This bit is not part
> of the physical_mask and is not preserved during mprotect(). As a
> result, the 'shared' bit is lost during mprotect() on shared mappings.
>
> _COMMON_PAGE_CHG_MASK specifies which PTE bits need to be preserved
> during modification. AMD includes 'sme_me_mask' in the define to
> preserve the 'encrypt' bit.
>
> To cover both Intel and AMD cases, include 'cc_mask' in
> _COMMON_PAGE_CHG_MASK instead of 'sme_me_mask'.
>
> Signed-off-by: Kirill A. Shutemov <[email protected]>
> Fixes: 41394e33f3a0 ("x86/tdx: Extend the confidential computing API to
> support TDX guests")
> Cc: Tom Lendacky <[email protected]>
> Cc: Chris Oo <[email protected]>
> Cc: Dexuan Cui <[email protected]>
Reviewed-by: Rick Edgecombe <[email protected]>
So does this mean there is shared memory mapped to userspace? Or is this a
theoretical correctness thing?
On Fri, Apr 12, 2024 at 08:48:56PM +0000, Edgecombe, Rick P wrote:
> On Fri, 2024-04-12 at 22:12 +0300, Kirill A. Shutemov wrote:
> > The TDX guest platform takes one bit from the physical address to
> > indicate if the page is shared (accessible by VMM). This bit is not part
> > of the physical_mask and is not preserved during mprotect(). As a
> > result, the 'shared' bit is lost during mprotect() on shared mappings.
> >
> > _COMMON_PAGE_CHG_MASK specifies which PTE bits need to be preserved
> > during modification. AMD includes 'sme_me_mask' in the define to
> > preserve the 'encrypt' bit.
> >
> > To cover both Intel and AMD cases, include 'cc_mask' in
> > _COMMON_PAGE_CHG_MASK instead of 'sme_me_mask'.
> >
> > Signed-off-by: Kirill A. Shutemov <[email protected]>
> > Fixes: 41394e33f3a0 ("x86/tdx: Extend the confidential computing API to
> > support TDX guests")
> > Cc: Tom Lendacky <[email protected]>
> > Cc: Chris Oo <[email protected]>
> > Cc: Dexuan Cui <[email protected]>
>
> Reviewed-by: Rick Edgecombe <[email protected]>
>
> So does this mean there is shared memory mapped to userspace? Or is this a
> theoretical correctness thing?
Drivers can do this. Things like VFIO, I guess.
I think I should have credited Chris for reporting and testing the problem:
Reported-and-tested-by: Chris Oo <[email protected]>
--
Kiryl Shutsemau / Kirill A. Shutemov
On 4/12/24 12:12 PM, Kirill A. Shutemov wrote:
> The TDX guest platform takes one bit from the physical address to
> indicate if the page is shared (accessible by VMM). This bit is not part
> of the physical_mask and is not preserved during mprotect(). As a
> result, the 'shared' bit is lost during mprotect() on shared mappings.
>
> _COMMON_PAGE_CHG_MASK specifies which PTE bits need to be preserved
> during modification. AMD includes 'sme_me_mask' in the define to
> preserve the 'encrypt' bit.
>
> To cover both Intel and AMD cases, include 'cc_mask' in
> _COMMON_PAGE_CHG_MASK instead of 'sme_me_mask'.
>
> Signed-off-by: Kirill A. Shutemov <[email protected]>
> Fixes: 41394e33f3a0 ("x86/tdx: Extend the confidential computing API to support TDX guests")
> Cc: Tom Lendacky <[email protected]>
> Cc: Chris Oo <[email protected]>
> Cc: Dexuan Cui <[email protected]>
> ---
Looks good to me.
Reviewed-by: Kuppuswamy Sathyanarayanan <[email protected]>
> arch/x86/include/asm/pgtable_types.h | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
> index 3f648ffdfbe5..7dd2fdfacff3 100644
> --- a/arch/x86/include/asm/pgtable_types.h
> +++ b/arch/x86/include/asm/pgtable_types.h
> @@ -148,7 +148,7 @@
> #define _COMMON_PAGE_CHG_MASK (PTE_PFN_MASK | _PAGE_PCD | _PAGE_PWT | \
> _PAGE_SPECIAL | _PAGE_ACCESSED | \
> _PAGE_DIRTY_BITS | _PAGE_SOFT_DIRTY | \
> - _PAGE_DEVMAP | _PAGE_ENC | _PAGE_UFFD_WP)
> + _PAGE_DEVMAP | _PAGE_CC | _PAGE_UFFD_WP)
> #define _PAGE_CHG_MASK (_COMMON_PAGE_CHG_MASK | _PAGE_PAT)
> #define _HPAGE_CHG_MASK (_COMMON_PAGE_CHG_MASK | _PAGE_PSE | _PAGE_PAT_LARGE)
>
> @@ -173,6 +173,7 @@ enum page_cache_mode {
> };
> #endif
>
> +#define _PAGE_CC (_AT(pteval_t, cc_mask))
> #define _PAGE_ENC (_AT(pteval_t, sme_me_mask))
>
> #define _PAGE_CACHE_MASK (_PAGE_PWT | _PAGE_PCD | _PAGE_PAT)
--
Sathyanarayanan Kuppuswamy
Linux Kernel Developer